A smart utility network (SUN) is a low rate (40 kb/s to 1 Mb/s), low power wireless technology that is specifically designed to be used in utility metering applications, such as transmitting electric, gas, or water usage data from the meter(s) on the customer premises to a data collection point (hub) operated for the utility. For example, meters could be installed for each house in a residential neighborhood, and then the data could be sent every 15 minutes from each meter to a pole-top data collection point. This data collection point could then be connected by fiber, copper wire, or wireless to a central office which collects all the data for a region. Data could either be sent directly from each meter to the collection point (star configuration), or it could be hopped from meter to meter until it reaches the collection point (mesh configuration).
There are different physical layers (PHYs) that can be used for a SUN including FSK (frequency shift keying), DSSS (direct sequence spread spectrum), and OFDM (orthogonal frequency division multiplexing). In a closed utility network the devices that are allowed into the network can be controlled by the utility or the network operator.
IEEE (Institute of Electrical and Electronics Engineers) 802.15 is a working group of the IEEE 802 standards committee which specifies Wireless Personal Area Network (WPAN) standards. IEEE 802.15.4 is a standard that specifies the physical layer and media access control for low-rate wireless personal area networks (LR-WPANs). It is the basis for the ZigBee, ISA100.11a, WirelessHART, and MiWi specifications, each of which further extends the standard by developing the upper layers which are not defined in IEEE 802.15.4. Alternatively, it can be used with 6LoWPAN (Internet Protocol version 6 low power wireless personal area network) and standard Internet protocols to build a wireless embedded Internet. The IEEE 802.15.4 g standard is commonly referred to as the Smart Utility Network (SUN) and is a physical layer (PHY) amendment to the existing low power, personal area network 802.15.4 standard. IEEE 802.15.4 g is intended to provide a global standard that facilitates very large scale process control applications such as the utility smart-grid network capable of supporting large, geographically diverse networks with minimal infrastructure, with potentially millions of fixed endpoints.
A SUN network can be set up in a mesh configuration where devices can communicate with neighbor devices rather than just with a hub. This helps to increase coverage since communication can be achieved even if the link directly to the hub is not good. However, this can increase the amount of traffic that goes through some devices since they have to include packet data from their neighbors as well as their own data. A mesh network can be appropriate for an urban or suburban area with a high density of meters and non-line-of-sight conditions between meters so that communication links between some meters and a hub is poor.
A star configuration is one where a hub communicates directly with each meter. This could be appropriate for rural environments when the density of meters is low so that there may not be a convenient neighbor to use as an intermediate hop. A mix between a star and mesh configuration can also be used in some deployments.
In a one-way system, readings “bubble up” from end devices (such as meters), through the communication infrastructure, to a “master station” which publishes the readings. A one-way system might be lower-cost than a two-way system, but also is difficult to reconfigure should the operating environment change.
In a two-way system, both outbound and inbound traffic is supported. Commands can be broadcast from a master station (outbound) to end devices, such as meters, that may be used for control and reconfiguration of the network, to obtain readings, to convey messages, etc. The device at the end of the network may then respond (inbound) with a message that carries the desired value. Outbound messages injected at a utility substation will propagate to all points downstream. This type of broadcast allows the communication system to simultaneously reach many thousands of devices. Control functions may include monitoring health of the system and commanding power shedding to nodes that have been previously identified as candidates for load shed. PLC (power line communication) also may be a component of a Smart Grid.
In packetized communication systems, packet arrival instants are generally random and unknown at the receiver. The payload can be successfully demodulated provided the receiver has symbol timing, frequency and phase offset information, in addition to achieving frame synchronization. In many practical applications, these parameters are not known a priori at the receiver and hence have to be estimated from the received signal. IEEE 802.15.4 g uses a DSSS preamble at the beginning of each DSSS packet.
The radio frequency channel can be very hostile. Channel characteristics and parameters can vary with frequency, location, time, and with radio interference from other devices.
Since meters have a long life span such as 20 years, there may be many generations of meters deployed in a utility network. The earlier deployed meters can be termed as legacy equipment. Therefore, smart meters using newer technology may need to co-exist with legacy devices. For example, the legacy devices in a utility network may communicate using FSK (frequency shift keying) modulation, often at a fixed data rate such as 50 kb/s, 100 kb/s or 150 kb/s.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.